The present invention is directed to valves, and in particular globe valves.
Globe valves are used for many applications, including as instrument valves for high pressure fluids such as oil and gas. Globe valves comprise a main body having an inlet, an outlet, and a passage between the inlet and the outlet. A bonnet is threaded onto the body and a stem is rotatable by a handle on the stem for opening and closing the passage.
A problem that has been experienced when opening a globe valve by rotating the stem is that the bonnet can be backed out of the body. This has resulted in inadvertent release of fluids having pressures as high as 6,000 to 10,000 psi, and has resulted in injury to operating personnel. Explosions can occur when the high pressure fluid is oil.
To overcome this problem, external releasable clamps are used to hold the bonnet to the body. However, when a valve having this clamp is disassembled for repair, often the clamp is not replaced, thereby destroying the safety mechanism. In operation, such a valve without the clamp replaced has had the bonnet backed off from the body and this has resulted in serious injury.
Although it is possible to design a valve where the bonnet can never be released from the body, such a valve would be wasteful in that it would be impossible to replace the packing, the washers of the valve, and to reseat the valve. Thus, instead of repairing the valve, it would be necessary to discard it.
Another problem with conventional valves is that the bonnet is swaged over the stem to prevent the stem from being turned out of the bonnet. However, this technique can fail, with resultant unexpected removal of the stem from the bonnet and escape of high pressure fluids.
In view of these problems, there is a need for a valve that includes a mechanism that prevents the bonnet from being unintentionally backed off, where the mechanism is an integral part of the valve and cannot be discarded when the valve is reassembled, and where the mechanism allows the bonnet to be removed from the body for repair of the valve. There is also need for a valve where the stem cannot be rotated out of the bonnet.